Each year many thousands of children and adults are injured in playgrounds, and in public and private recreation and sports facilities, due to falls on inadequately prepared surfaces. Lawsuits in which damages reach several million dollars are common where playground accidents have occurred. Insurance companies are being much more selective in granting coverage and, in some instances, are denying liability protection to institutions.
According to the U.S. Consumer Product Safety Commission more than 150,000 persons are injured each year on playgrounds in the United States. The need for a systematic and consistent means for evaluating the surface materials and to provide accessibility by handicapped individuals to playgrounds has been further amplified by the passage of the Americans With Disabilities Act.
There is an increased awareness of the need for playground safety, not only because of the litigation and because of direct government intervention, but also because institutions are recognizing that something needs to be done.
In many instances, there are materials that currently exist that will adequately protect the children and adults from damage. Some proposed methods to test these materials are extremely expensive, however, and others are relatively cheap. No uniform guidelines exist as to amounts and thickness of these materials, to reduce the desired safe level of acceleration in the event of a fall. Accordingly, each installation must be evaluated both as it is installed and over a period of time as constant use by playground users may change the properties of the installed surface.
A method and apparatus for determining the suitability of playground, recreation and sports facility surfaces has been provided in HOGAN, et al U.S. Pat. No. 4,856,318. The apparatus includes a transducer module consisting of an impact head and a transducer capable of converting impact forces to electrical signals. The device also includes an electronic module which detects the electrical signal from the transducer, processes it and converts it to a numerical reading. In the HOGAN Patent, a transducer is fixed to an impact head mass along a vertical center line which is on or slightly above the center of gravity. The transducer produces an electrical output signal at the moment of impact that is proportional to the peak impact G-level. This signal is detected at its peak, and operated on to covert the signal to a G-level indication.
Devices of the type described in the HOGAN Patent have been successful at least for preliminary data sampling. However, the device is severely limited for several reasons. First, it is very directional and does not produce a true reading unless the drop is truly on the perpendicular axis. Also, there often are significant variations in surface levelness. As a result, there really is no way to be sure that the drop was within the linear limits of the device. Multiple drops will generally produce a consistent or average reading if the drops are all within .+-.5% of the vertical. However, if the surface is not truly horizontal, then even truly vertical drops are not able to produce acceptable data.
It has now been discovered that merely measuring the gravitational force generated by impact of a device on a surface without being able to process the information to produce meaningful interpretive results is not enough to fully evaluate the surface. For example, in addition to the maximum gravitational force seen during the impact, the duration of the impact is also of interest. Specifically, the gravitational force as a function of the impact time produces what is known as a severity index (SI), which is the force measured divided by the amount of time needed to generate the maximum impact force. The United States Consumer Product Safety Commission Playground Safety Handbook now recommends a surface resiliency for playgrounds of 200 g, a SI of 1,000 and a head injury criteria value (HIC) of 1,000. While the calculation of an HIC value for a given drop involves complicated mathematical calculations, it would be desirable to make the measurements necessary for such calculations and, hopefully, be able to store sufficient data for the series of calculations.
Accordingly, it is the object of this invention to provide a testing device for surfaces subject to impact which is capable of producing reproducible accurate values relating to the impact.
Another object of this invention is to provide such a device which can accommodate variation in the relationship of the surface to the horizontal.
Yet another object is to provide a device which is capable of measuring and storing the data necessary to calculate specific head injury criteria as defined by various government and safety agencies. Other objects will appear hereafter.